The purpose of a tail on a two-legged creature is generally to act as a counter balance, often for running, as it is with most two-legged dinosaurs like the tyranosaurus. This means that catgirls have tails to allow them to maintain balance even when they are very top/front-heavy.

I think the main problem to him (her?) is that a tail would make some sexual positions rather uncomfortable for the girl. We humans have (for example) the missionary position or any other position where we look at each other because we don't have tails getting in the way. Counter-balance good and nice, but remember what's more important.

The only thing i get when i google planet of the cat is
some old thing that are in no way related to this (art wise , and date of creation )along with stupid youtube video and the neko no wakusei search only lead me to dozen of blog with cat pictures ...

Hello ladies... Look at your housecat. Now back at me. Now back at your cat. Now back at me. Sadly, your cat is not me... but it could smell like me if... Well, best not go there. tl;dr, a cat is fine too...

It seems the keyword to put into Sankaku Channel is either "neko_no_wakusei" or "mamecchi", but there's not much yet. Sadly, I can't find the actual books anywhere, but it looks like it'll be an art book.